Emergency and standby power in hospitals

Consulting engineers who specify emergency power equipment understand that installations for hospitals are required to comply with NFPA 110 in conjunction with NFPA 70. System designers must interpret the requirements of these standards, ensure their designs follow them, and educate their clients about how the standard affects their operations.


This article is peer-reviewed.Learning Objectives:

  • Explain the codes and standards that electrical engineers should review as they design hospitals.
  • Apply NFPA 110, 101, 70, 99, and other relative codes for emergency and standby power systems.
  • Analyze the complexity of hospital electrical and power system design. 

Hospitals have been evolving for the past few decades in both size and complexity, and in many cases have grown from a single structure to multiple buildings in a campus setting. A primary challenge for many health care facilities is to provide a high-quality source of electrical power that is backed up with highly reliable emergency and standby power systems to ensure uninterrupted flow of electricity to the entire facility, particularly during crisis and natural disasters.

Figure 1: This diagram highlights a distribution system for essential electrical system types per NFPA 99. Courtesy: Arup

The terminology used for backup (emergency and standby) power systems in health care facilities is different than other facilities. It is designated as the "essential electrical system" per NFPA 70: National Electrical Code (NEC) Article 517, which is consistent with the terminology and requirements stated in NFPA 99: Health Care Facilities Code.

Most buildings experience power interruptions that are caused by utility outages, equipment failures, testing, and maintenance, and generally are easier to manage due to the cause, timing, and duration. In many cases, these power outages are planned and easily handled. However, power outages due to natural disasters and unexpected events are much more difficult to deal with, and in some cases the entire facility has to rely solely on the emergency and standby power system to continue operating for several days.

Unlike most standard commercial buildings, delivering emergency and standby power to health care facilities is a major undertaking due to its complexity and size. It involves many different systems consisting of alternate sources of power, switching equipment, controls, and distribution equipment.

Codes and standards

There are several codes and standards that govern emergency power requirements for the hospitals, including:

NFPA 99: It establishes the minimum criteria for the installation, performance, and operation of a wide range of systems and equipment in health care facilities to ensure the safety of patients, staff, and the public from electrical failures, fires, and other hazards. After 7 yr of review and discussion, the 2005 edition went through extensive changes in both content and format to transition from a "standard" to a "code" for the 2012 edition. The most important change was to introduce a risk-based approach in lieu of an occupancy-based approach to better deal with the risk posed to the patients and health care personnel, and not the occupancy or building type. The recently released 2015 edition has incorporated a few more modifications to clarify and make the performance criteria more practical so that it could be easily adopted and enforced.

The essential electrical system (EES) requirements can be found in NFPA 99, Chapter 6; these describe two different EES requirements (Type 1 or 2) that correlate to different risk categories (Categories 1 through 4) defined in Chapter 4. EES requirement Type 3 was eliminated in the 2015 edition because Category 3 and 4 spaces are no longer required to be served by an EES. The Category 1 spaces require EES Type 1 service while Category 2 spaces require EES Type 2 service. There are very few differences between EES Types 1 and 2, other than their power-distribution system.

Hospitals, for the most part, fall under the risk Category 1, where equipment and systems are expected to work and be available at all times, and their failure is likely to cause major injury or death to patients, staff, or visitors. On the other hand, the Category 2 spaces are areas of the hospital where failure of equipment or a system is likely to cause minor injury to patients, staff, or visitors, but no risk to life.

Figure 2: This one-line diagram of a generator paralleling switchgear includes a split-bus system. Courtesy: Arup

The EES, depending on the EES requirements type, is divided into several branches (to be described later in this article), except for the grouping of branches that was modified in the 2012 edition of NFPA 99. The term "emergency system" (not the same emergency systems used in NEC Article 700) that was comprised of two separate branches (life safety and critical) was eliminated.

NFPA 70: The NEC went through its regular cycle of code revisions for the 2014 edition, and updated parts of "essential electrical system" to match with the NFPA 99-2012 terminology and designations for the separate branches. NFPA 70 does not address different types of EES or risk categories assigned to each space.

The "life safety" branch is the only system that needs to meet the requirements of NEC Article 700, except as amended by Article 517.

NFPA 70 Article 517 addresses all electrical requirements associated with health care facilities and is primarily based on the electrical requirements defined in NFPA 99. While the text in NFPA 99 outlines the performance requirements with regards to safety, Article 517 defines how the systems shall be installed to accomplish the desired level of performance.

NFPA 101: Life Safety Code: It defines the requirements for "illumination of means of egress" and "exit signs and emergency lighting" that have been referenced in both the NFPA 99 and the NEC as part of the "life safety" branch requirements.

In addition to "means of egress" requirements, NFPA 101 addresses the specific provisions applicable to high-rise buildings under section 11.8, which has some implications on the standby power system.

NFPA 110: Standard for Emergency and Standby Power Systems: It is referenced in all of the abovementioned codes for the requirements related to the emergency generators (alternate source of power) in terms of installation, testing, and maintenance.

This standard recognizes six classifications of emergency power supply systems (EPSSs), five types of EPSSs, and two levels of EPSS equipment.

  • Classification: Defines the minimum time of operation at full load without being charged or refueled.
  • Type: Defines the maximum time the load terminals of a transfer switch can be without acceptable electrical power.
  • Level: Defines the installation, performance, and maintenance requirements. Level 1 systems shall be installed where failure of an EPSS could result in loss of human life or serious injuries, and Level 2 systems are for an EPSS when failure to perform is less critical to human life and safety.

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